1. Field of the Invention
A new improved catalyst system for alpha-olefin type polymerizations includes at least one metal alkyl compound having the formula R.sub.n MR'.sub.3-n in combination with a Group IVB-VIII transition metal compound on a support and at least one Lewis base wherein R is selected from the group consisting of C.sub.3 to C.sub.20 secondary or tertiary alkyl, cycloalkyl, alkenyl or aralkyl groups; R' is selected from the group consisting of C.sub.1 to C.sub.20 primary alkyl, alkenyl or aralkyl groups, or a hydride, M is selected from the group consisting of aluminum, gallium or indium; and n=1-3. The improved catalyst system provides polymers having increased isotactic stereoregularity as well as lower catalyst residue.
2. Description of the Prior Art
There is extensive art on the polymerization of ethylene and higher alpha-olefins, including dienes, using Ziegler type catalysts containing either alkyl metals or alkyl metals in which an alkyl group has been replaced by X, OR", SR", NR".sub.2, etc., in combination with a transition metal compound of Groups IVB-VIII, where X=halide, and R"=C.sub.1 to C.sub.20 hydrocarbyl substituent.
It is well known to use various alkyl aluminum compounds in combination with transition metal compounds of Groups IVB-VIII in Ziegler-type polymerizations of alpha olefins. For stereospecific polymerization of propylene and higher alpha olefins, the most effective commercially used alkyl metal compounds are AlEt.sub.3 and AlEt.sub.2 Cl, although Al(n-Pr).sub.3, Al(n-Bu).sub.3, Al(i-Bu).sub.3 and Al(iBu).sub.2 H give similar results. Longer chain alkyl aluminums, such as Al(n-C.sub.6).sub.3, Al(n-C.sub.8).sub.3, (n-C.sub.8).sub.2 AlCl, etc., drastically reduce stereospecificity as shown by much lower heptane insolubles (Ziegler and Montecatini, Belgian Pat. No. 543,259). Thus it was surprising to find that larger secondary and tertiary alkyl groups produced higher stereospecificity in this invention.
This invention claims novel, improved alkyl metal cocatalysts for use with Groups IVB-VIII transition metal compounds for stereospecific polymerization of propylene and higher alpha olefins. The new cocatalysts are tri-organo metal compounds of aluminum, gallium or indium which contain at least one secondary or tertiary alkyl group. These cocatalysts yield higher activity and/or isospecificity than the conventional primary di- or tri-alkyl metal compounds when used in combination with the various types of supported transition metal catalysts, such as MgCl.sub.2 -supported TiCl.sub.4, supported TiCl.sub.3, etc., with or without other catalyst modifiers present, such as Lewis bases, alcohols, phenols, polymers, dispersants, binders and other additives.
A number of patents have been issued on the use of trialkyl metal compounds as cocatalyst for the polymerization of various monomers. However, these patents fail to teach, imply or infer the inventive concept of having at least one, preferably two, secondary or tertiary alkyl groups in the trialkyl metal compound in order to be able to achieve both increased polymerization activity and improved isotacticity of the resultant polymer when used in combination with supported transition metal catalysts. These patents which are non applicable to the instant invention are U.S. Pat. No. 3,953,414, Belgium No. 845,593, Belgium No. 846,314, German DT No. 2620-886, British No. 1,335,887, German DT No. 2630-585, British No. 1,140,659, German DT No. 2612-650, South African No. 7,503,470, German DT No. 2355-886, Japanese No. 51064-586, South African No. 7507-382, German DT No. 2638-429, Japanese No. 51057-789, U.S. Pat. No. 3,992,322, Japanese No. 52027-090, and U.S. Pat. No. 3,400,110.
Other patents which are non applicable to the instant invention are U.S. Pat. No. 4,039,472; British No. 1,489,599; British No. 1,490,509; Japanese No. 1136-625; JA No. 7008 982-R; and Belgium No. 735,291.